there are several kinds of cracks. This is a crack that occured during the firing process. But it might as well have happened duringthe drying process. Cracks like this can also occur when the pot is put into the kiln.One could write an entire book on all the mistakes that can happen.

I can't see it very good in the picture , but it does look pretty wide at the top which makes me think it cracked on the way up in firing ( possiblyfinely cracked in bisque but with all the cracks I think it would have been noted) , BUT it doesn't look as if any glaze flowed into the cracks or rounded the edges, SO, I'm going to guess it cracked during cooling.When mine crack it's usually during drying, or cooling.

Andy,Although its been a while since I have had any cracks in my pieces, I am sure with my new gas kiln I will be experiencing quite a few ( ), as can be expected with the learning curve. I lost probably two full (electric) kiln loads total in the early years, and it really taught me alot. The ruined piece forced me to reevaluate the pot, the processes I used to form it, and its firing.

I am guessing here, but it makes sense to me that this crack may have come from too big of a heat differential in the top portion of the pot. Whether this was from it cooling or heating too quick is what I would look into...

If it happened during the firing, your problem could stem from contaminated clay. This looks like a burn out of some sort. I have seen this type of coloration from large iron particles burning out of a clay body.

Looks like copper to me. I'm wondering if you had that same decoration on the other side that is cracked almost identical? If so, I'm still thinking it could be a prob from cooling speed where the copper is?Andy, how thick are your kiln walls? 3" ?Do you fire down your gas kiln?I think I remember you telling me once that you didn't. I ONLY fire down my electric kiln during inversion because it's fairly easy but I no longer high fire with the electric kiln, gas one only, and it's a PIA to fire-down my gas kiln so,I have a technique I've used for several years to slow cooling on my gas kiln without firing down. I'll PM you as it takes some explanation.Dale

Andy,It is fun to see some pots that just went wrong-- we all have them. Here is one that turned into a big slump because I forgot to wad up the bottom I appreciate your honest and open approach to this site and enjoyed your new video. Here is one of my recent failures and was a commission that I have to start over But... it happens.